Zinc coating appearance of a bluish-white, standard electrode potential is-0.76V, soluble in acid, alkali soluble, amphoteric metal is curved. Almost no change in the zinc dry air, zinc corrosion critical humidity is greater than 70%, therefore the role of carbon dioxide and oxygen in a humid atmosphere with a film composed of a layer mainly composed of basic zinc carbonate is generated, this layer must Inhibition The role of zinc and hydrogen sulfide from the sulfide-containing reaction of zinc sulfide; zinc is susceptible to chloride ion etching, it is unstable in seawater. Zinc in a confined or poorly ventilated, humid air conditions, volatile matter (low molecular weight carboxylic acids, aldehydes, phenols, ammonia, etc.) and non-metallic materials in contact, zinc vulnerable to corrosion, to generate white osteoporosis corrosion products, commonly known as " hoarfrost. " Zinc in high temperature, high humidity, confined conditions, contact with bakelite, paint, wood volatiles released, zinc filamentous single crystal growth tendency, commonly known as "Long Hair".
The standard potential of zinc negative than iron, steel is anodic coatings can provide reliable electrochemical protection. Iron and steel products used in the industrial atmosphere, rural atmosphere and ocean atmosphere can be selected protective layer of zinc for protection life almost zinc layer thickness is proportional to. All industrial air pollution in the atmosphere, the corrosion of the zinc coating is better than cadmium plating, on the contrary in the sea or sea water. Zinc coating chromate passivation, corrosion resistance can be increased to 6 - 8 times. Therefore, the passivation process is an essential step. In the passivation film the organic dyeing, can be used for the low file protection --- decorative coating. In order to reduce the thickness of the zinc coating can improve the corrosion resistance at home and abroad to adopt the following two measures: One is to raise the quality of the passive film, such as blue, green, military green, black passivation rainbow colors instead of the conventional passive film, especially military green passivation film corrosion resistance is preferably; second is thinner iron 0.3% - 0.6% Zn-Fe alloy, or nickel-containing 6% -10% of the Zn-Ni alloy was used instead of pure zinc coating, corrosion more than three times the performance, widely used in the car instead of galvanized steel plate. Use of the zinc coating temperature should not exceed 2500C, and zinc to crystallize at this temperature, tissue deformation, brittle hair, corrosion resistance is decreased. Corrosion, heat-resistant parts required to use the Zn-Ni alloy layer.
The galvanized electrolyte can be divided into alkaline and acidic two categories, the common presence or absence of cyanide zincate zinc, cyanide zinc, the ammonium salt galvanized, chloride zinc sulfate zinc and so on. Domestically, the non-cyanide zincate is still the mainstream. Chloride the galvanized and low cyanide bright zinc rapid development in recent years due to the improvement of the performance of the galvanized additives to improve, and the ammonium salt galvanized continue to decline. Select the bath plated pieces of material, shape, appearance requirements, such as stamping small pieces and complex parts, in particular the need the auxiliary anode deep hole or tubular member should be selected alkaline bath; sensitive to hydrogen embrittlement parts is appropriate weak acid zinc plating solution. When two different bath, the production is very beneficial.
